Dicotyledon plant cultivation method and dicotyledon plant cultivation device

Abstract

To provide a plant cultivation method that makes it possible to increase plant growth speed by irradiation with high-illuminance light while suppressing the occurrence of a photoinhibition or photoprotection reaction in the plant.SOLUTION: Provided is a dicotyledon plant cultivation method in which light 3 of a wavelength in a red region that is included in the wavelength band for the absorption peak of chlorophyll a is applied to a dicotyledon plant 4. The light 3 is emitted from a laser light source 1, does not include light of a wavelength outside the wavelength band for the absorption peak of the chlorophyll a, and, at the point of arrival at the dicotyledon plant 4, has a photon flux density (PPFD) which is a predetermined value or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for growing plants.

Background Art

[0002] It is known that a plurality of types of chlorophyll are contained in plant leaves, and chlorophyll a is mainly used for photosynthesis. Chlorophyll a has a peak in the light absorption spectrum near 660 nm in the red region.

[0003] In a light source used for growing plants, in order to improve the efficiency of plant photosynthesis, for example, in Patent Document 1, a light source having emission peaks in a first wavelength range of 600 nm or more and 700 nm or less and a second wavelength range of 720 nm or more and 800 nm or less is proposed. This light source is designed such that the ratio (d2 / d1) of the photon flux density (d2) in the second wavelength range to the photon flux density (d1) in the first wavelength range is 0.1 or more. As the light-emitting element constituting the light source, in addition to an LED (light-emitting diode), an LD (laser diode) can be used, as disclosed in Patent Document 1 (see paragraph 0050 of Patent Document 1).

[0004] On the other hand, Patent Document 2 proposes cultivating plants by irradiating plants with light in a specific wavelength band by combining a narrow-band band-pass filter with a white light source. As the specific wavelength band, the wavelength showing the maximum transmittance is shown to be 400 nm or more and 500 nm or less, or 630 nm or more and 700 nm or less.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, in the technology of Patent Document 1, a light source having emission peaks in each of a first wavelength range of 600 nm or more and 700 nm or less and a second wavelength range of 720 nm or more and 800 nm or less is proposed. In the technology of Patent Document 2, it is proposed to irradiate light having a wavelength of 400 nm or more and 500 nm or less, or 630 nm or more and 700 nm or less.

[0007] Since the peak bands of the light absorption spectrum of chlorophyll a are in the band from around 600 nm to around 700 nm and the band from around 300 nm to around 450 nm, the light bands of Patent Documents 1 and 2 almost match the peak bands of the absorption spectrum of chlorophyll a.

[0008] On the other hand, according to the research of the inventors, even when irradiating light with a wavelength that matches the peak band of the absorption spectrum of chlorophyll a, if the illuminance is increased to increase the growth rate of plants, when a certain illuminance is reached, the relative growth rate (RGR) saturates, and it is suggested that when irradiating light with an illuminance above the saturated illuminance, a phenomenon in which the leaf color changes depending on the type of plant occurs. These phenomena are considered to be caused by a decrease in photosynthetic function called "photoinhibition" and a "photoprotective reaction", which is a mechanism by which plants process excess light energy.

[0009] An object of the present invention is to provide a method for growing plants that can suppress the occurrence of photoinhibition and photoprotective reactions in plants while irradiating high-illuminance light to increase the growth rate of plants.

Means for Solving the Problems

[0010] In order to achieve the above object, according to the present invention, there is provided a method for growing dicotyledonous plants by irradiating light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a toward the dicotyledonous plants. This light is light emitted from a laser light source, does not include light having a wavelength outside the wavelength band of the absorption peak of chlorophyll a, and the photosynthetic photon flux density (PPFD) at the time when it reaches the dicotyledonous plants is equal to or greater than a predetermined value.

Effects of the Invention

[0011] According to the present invention, since the light irradiated to the plants is light emitted from a laser light source, the wavelength band is narrow, and even when irradiating high-intensity light, it is possible to suppress the occurrence of photo-inhibition and light defense reactions in the plants, so that the growth rate of the plants can be increased.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] An embodiment of the present invention will be described below.

[0014] In this embodiment, dicotyledonous plants are grown by irradiating light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a toward the dicotyledonous plants.

[0015] For example, as shown in FIG. 1, a dicotyledonous plant growing apparatus 100 is used, which is a combination of a laser light source 1 in a predetermined wavelength band and an optical element 2 that irradiates the entire dicotyledonous plant with the laser light 3 emitted from the laser light source 1.

[0016] The laser light 3 emitted from the laser light source 1 is light having a wavelength in the red region. This laser light 3 passes through the optical element 2 and does not contain light having a wavelength other than a predetermined wavelength band (specifically, 640 nm or more and 675 nm or less) including the absorption peak of chlorophyll a (see FIG. 2)) when irradiating the plant 4. Moreover, the photosynthetic photon flux density (PPFD) at the time of reaching the dicotyledonous plant is equal to or higher than a predetermined value at which physiological damage occurs to the dicotyledonous plant if it is light having a wavelength other than the above-mentioned predetermined wavelength band.

[0017] As shown in FIG. 3, the wavelength band of the emission spectrum of the laser light 3 preferably includes the absorption peak of chlorophyll a (specifically, 660 nm). Further, the spectrum of the laser light 3 is preferably a steep spectrum with a full width at half maximum of 5 nm or less. To achieve these, it is preferable that there is one type of laser light source 1, and the central wavelength is preferably around 660 nm.

[0018] In addition, the dicotyledon cultivation device 100 may irradiate the dicotyledon 4 with two types of laser light having different central wavelengths as long as it is within the wavelength band of the absorption peak of chlorophyll a.

[0019] The laser light 3 does not contain light outside the wavelength band of 640 nm or more and 675 nm or less as described above, but preferably does not contain light outside the wavelength band of 645 nm or more and 670 nm or less.

[0020] The photosynthetic photon flux density (PPFD) at the time when it reaches the dicotyledon 4 is preferably 150 μmolm -2 s -1 or more.

[0021] As the optical element 2, for example, a diffusion plate can be used. Since the laser light 3 does not have to have the same phase when it reaches the dicotyledon 4, an optical element 2 having an unaligned phase of the laser light 3 may be used.

[0022] Thus, in this embodiment, by irradiating and growing the entire dicotyledon 4 with the laser light 3 having predetermined wavelength characteristics, even when the photosynthetic photon flux density (PPFD) at the time when it reaches the dicotyledon 4 is high, the dicotyledon 4 can suppress the occurrence of "photoinhibition" in which chlorophyll a is inactivated under high illumination and the occurrence of a "light defense reaction" such as the expression of pigments that the plant defends itself from high-intensity light. As a result, with the cultivation method of this embodiment, it becomes possible to grow the dicotyledon 4 with high-intensity light, and an improvement in yield by forced cultivation can be expected.

[0023] <Modification Example 1> The plant cultivation method of the above embodiment is a method of cultivating by irradiating dicotyledonous plants with light having a wavelength in the red region. However, in addition to the light in the red region, light in the blue region other than the red region may be irradiated. For example, as shown in FIG. 4, the dicotyledonous plant cultivation apparatus 100 is configured to further include a light source 5 that emits light 7 in the blue region in addition to the laser light source 1 that emits laser light 3 having a wavelength in the red region. An optical element 6 that irradiates the entire dicotyledonous plant 4 with the light 7 from the light source 5 may be disposed between the light source 5 and the dicotyledonous plant 4.

[0024] The wavelength of the light 7 in the blue region may be narrow-band laser light. Further, the light 7 may be light having a wider band than the laser light emitted from a light-emitting element such as an LED, not limited to laser light. <Modification 2> In the above embodiment, the optical element 2 of the dicotyledonous plant cultivation apparatus 100 may be configured to be able to irradiate the entire dicotyledonous plant 4 with the laser light 3, and is not limited to a diffusion plate, and an element such as a polygon mirror that scans the laser light may be used (see FIG. 5). Further, a mechanism for relatively moving the light source 1 with respect to the plant can also be used as the optical element 3.

[0025] <Modification 3> In the above embodiment, as the optical element 2 of the dicotyledonous plant cultivation apparatus 100, a combination of a light guide plate 22 having a diffuser and a reflective film and a polygon mirror 21 can also be used (see FIG. 6). The laser light emitted from the laser light source 1 is reflected by the polygon mirror 21 to form a line beam, which is incident from the end face of the light guide plate 22, scattered while guiding through the light guide plate 22, and irradiated from the lower surface toward the dicotyledonous plant 4 by the reflective film.

[0026] <Modification 4> In the above embodiment, as the optical element 2, a plurality of optical fibers 24 whose emission ends are arranged two-dimensionally can also be used (see FIG. 7).

[0027] The light emitted from the laser light source 1 is made incident on a plurality of arranged optical fibers 24 using a branching element (not shown) or the like, emitted from the emission ends of the plurality of optical fibers 24, and irradiated onto the dicotyledonous plant 4. As a result, since it can be emitted from the emission ends of the plurality of two-dimensionally arranged optical fibers 24, the laser light 3 emitted from the laser light source 1 can be irradiated onto the entire dicotyledonous plant.

Example

[0028] Examples 1, 2, and 3 of the present invention will be described. In Examples 1, 2, and 3, an LD (laser diode) having a wavelength peak of 660 nm and a half-value width of 1.6 nm was used as the laser light source 1, a diffusion plate capable of expanding the irradiation range of the laser light was used as the optical element 2, and the laser light 3 was continuously irradiated for 12 days by the cultivation method of the embodiment to grow the dicotyledonous plant 4. Note that the optical element 2 may be built in the apparatus of the laser light source 1. The grown dicotyledonous plants 4 are tobacco and lettuce (Red Fire), as shown in Table 1. The photosynthetic photon flux density (PPFD) of the laser light 3 at the time of reaching the dicotyledonous plant 4 was 150 μmolm -2 s -1 and 300 μmolm -2 s -1 There were two types.

[0029] Also, as Comparative Examples 1, 2, and 3, an LED having a wavelength peak of 660 nm and a half-value width of 17 nm was used as the light source, and other conditions were the same as those in Examples 1, 2, and 3 to grow the dicotyledonous plant 4.

Table 1

[0030] Photographs of the appearance of dicotyledonous plants grown in Examples 1 and 2 and Comparative Examples 1 and 2, and the measurement results of photosynthetic activity, light irradiation stress, dry weight of leaves, and leaf area are shown in Fig. 8. The photosynthetic activity and light irradiation stress shown in Fig. 8 are measurement results obtained using the IMAGING-PAM M-series of WALZ. The dry weight was measured after putting the sampled plants into a dryer to remove the moisture in the plants and then returning them to room temperature. The leaf area was measured by image processing to extract only the leaves from the photographed images of the leaves.

[0031] As is clear from the appearance photographs in Fig. 8, the tobacco grown in Example 1 had a larger leaf area than the tobacco grown in Comparative Example 1. Also, the tobacco grown in Example 1 had no leaf discoloration, while the leaves of the tobacco grown in Comparative Example 1 were discolored.

[0032] Similarly, the lettuce (Red Fire) grown in Example 2 had a larger leaf area than the lettuce grown in Comparative Example 2. Also, the lettuce grown in Example 2 had no leaf discoloration, while the leaves of the lettuce grown in Comparative Example 2 had turned red-purple.

[0033] Also, as is clear from the fluorescence imaging images of chlorophyll a by the Imaging PAM method shown in Fig. 8, it was confirmed that the numerical value of the photosynthetic activity of the grown dicotyledonous plants was higher for the tobacco grown in Example 1 than for the tobacco grown in Comparative Example 1. Also, the numerical value of the photosynthetic activity of the lettuce grown in Example 2 was equivalent to that of the lettuce grown in Comparative Example 2.

[0034] The dry weight of the leaves of the tobacco grown in Example 1 was about twice that of Comparative Example 1. The dry weight of the leaves of the lettuce grown in Example 2 was about 1.5 times that of Comparative Example 2.

[0035] The leaf area of the tobacco grown in Example 1 was about twice that of Comparative Example 1. The leaf area of the lettuce grown in Example 2 was about 1.5 times that of Comparative Example 2.

[0036] In Comparative Example 2, the leaves turned red-purple because a light defense reaction occurred due to the accumulation of anthocyanin. Lettuce (Red Fire) is known to accumulate anthocyanin as a reaction to light stress.

[0037] In addition, external photographs of the lettuce grown in Example 3 and Comparative Example 3 are shown in Fig. 9. When the photosynthetic photon flux density (PPFD) is 300 μmolm -2 s -1 , similar to Example 2 and Comparative Example 2 where the photosynthetic photon flux density (PPFD) is 150 μmolm -2 s -1 The leaf area of the lettuce in Example 3 was larger than that of the lettuce grown in Comparative Example 3. Also, the lettuce grown in Example 3 had no leaf discoloration, while the leaves of the lettuce grown in Comparative Example 3 were red-purple.

[0038] From these results, it can be seen that in Comparative Examples 1, 2, and 3, photo-inhibition occurred where photosynthetic activity decreased due to the decomposition of chlorophyll, etc., and in Comparative Example 2, a light defense reaction of lettuce occurred, but in Examples 1, 2, and 3, photo-inhibition and light defense reactions did not occur. This phenomenon is because in Comparative Examples 1, 2, and 3, the half-value width of the LED used as the light source was wide, so wavelength components outside the absorption peak of chlorophyll a caused photo-inhibition and light defense reactions in dicotyledonous plant 4, but in Examples 1, 2, and 3, since the laser light source 1 was used, the half-value width was narrow and the wavelength components outside the absorption peak of chlorophyll a were extremely small, so it can be estimated that photo-inhibition and light defense reactions did not occur.

[0039] From these facts, it can be estimated that when irradiating light with a wavelength deviated from the absorption peak of chlorophyll, there are extra light components that cannot be completely absorbed by chlorophyll, and photo-inhibition or a light defense reaction is shown.

[0040] Even for light with a wavelength deviated from the absorption peak of chlorophyll, the range in which the photosynthesis rate does not decrease is considered to be the wavelength range that does not cause photo-inhibition or a photo-defense reaction. Therefore, in order to determine this wavelength range, the photosynthesis rate when irradiating tobacco with laser light 3 from four types of laser light sources 1 (LD) with central wavelengths of 637 nm, 659 nm, 675 nm, and 690 nm was measured using a photosynthesis transpiration measurement device (LI-6400XT manufactured by Licor). Fig. 10 shows a graph plotting the photosynthesis rate for each wavelength.

[0041] The photosynthesis rate in Fig. 10 was normalized, and fitting was performed by the least squares method as a quadratic equation of wavelength λ, and an approximate equation for the photosynthesis rate shown in the following formula (1) was obtained.

[0042] Normalized photosynthesis rate = -0.00149λ 2 +1.96046λ - 639.37411 ···(1)

[0043] Fig. 11 shows a plot of the above formula (1). Also, from Fig. 11, it can be seen that the wavelength indicating the peak value of the photosynthesis rate is very close to 660 nm, which is the absorption peak of chlorophyll a. In addition, Fig. 11 shows the wavelengths (645 nm, 670 nm) indicating 95% of the photosynthesis rate and the wavelengths (640 nm, 675 nm) indicating 90% of the photosynthesis rate with respect to the peak value of the photosynthesis rate.

[0044] From Fig. 11, it was confirmed that if the wavelength range of the laser light 3 irradiated on the dicotyledonous plant 4 is the wavelength band (640 - 674 nm) showing a photosynthesis rate up to 90% with respect to the peak value of the photosynthesis rate, the decrease in the photosynthesis rate with respect to the peak value is small. In particular, it was confirmed that the wavelength band (644 - 671 nm) showing a photosynthesis rate up to 95% has an even smaller decrease in the photosynthesis rate with respect to the peak value. By irradiating the laser light 3 in these wavelength bands 640 - 674 nm (especially 644 - 671 nm), almost no photo-inhibition or photo-defense reaction appears in the plant even under high illuminance, and an improvement in yield by forcing cultivation etc. is expected.

[0045] The technologies of this embodiment and examples can be used for plant cultivation in horticulture and vegetable cultivation. For example, they can be applied to a plant growth light source device (such as for a plant factory) and a light source device for protected horticulture (including a supplementary light source).

Explanation of Signs

[0046] 2 Optical element 3 Laser light 4 Dicotyledonous plant 5 Light source 6 Optical element 21 Polygon mirror 22 Light guide plate 24 Optical fiber 100 Dicotyledonous plant cultivation device

Claims

1. A method for growing dicotyledonous plants by irradiating light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a toward the dicotyledonous plants, wherein the light is light emitted from a laser light source, does not include light having a wavelength outside a predetermined wavelength band including the absorption peak of chlorophyll a, and the photosynthetic photon flux density (PPFD) at the time of reaching the dicotyledonous plants is a predetermined value or more. A method for growing dicotyledonous plants, characterized by the above.

2. The method for growing dicotyledonous plants according to claim 1, wherein the wavelength band of the laser light includes the absorption peak of the chlorophyll a. A method for growing dicotyledonous plants, characterized by the above.

3. The method for growing dicotyledonous plants according to claim 1, wherein the predetermined wavelength band is a band of 640 nm or more and 675 nm or less. A method for growing dicotyledonous plants, characterized by the above.

4. The method for growing dicotyledonous plants according to claim 3, wherein the predetermined wavelength band is a band of 645 nm or more and 670 nm or less. A method for growing dicotyledonous plants, characterized by the above.

5. The method for growing dicotyledonous plants according to claim 1, wherein the full width at half maximum of the spectrum of the laser light is 5 nm or less. A method for growing dicotyledonous plants, characterized by the above.

6. The method for growing dicotyledonous plants according to claim 1, wherein the laser light source is of one type. A method for growing dicotyledonous plants, characterized by the above.

7. A method for growing dicotyledonous plants according to claim 1, wherein the predetermined photosynthetic photon flux density (PPFD) is 150 μmol m －２ s －１ or more, characterized by a method for growing dicotyledonous plants.

8. The method for growing dicotyledonous plants according to claim 1, wherein the dicotyledonous plants are tobacco or lettuce. A method for growing dicotyledonous plants, characterized by the above.

9. A laser light source that emits laser light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a, and an optical element that irradiates the entire dicotyledonous plants with the laser light, wherein the laser light emitted from the laser light source does not include light having a wavelength outside a predetermined wavelength band including the absorption peak of chlorophyll a, and when the entire dicotyledonous plants are irradiated with the optical element, the intensity is equal to or higher than a predetermined photosynthetic photon flux density (PPFD) at which physiological disorders occur in the dicotyledonous plants. A dicotyledonous plant growing apparatus, characterized by the above.

10. The dicotyledon plant cultivation device according to claim 9, wherein the optical element is any one of a diffusion plate that diffuses laser light, an element that scans laser light, a light guide plate that diffuses while guiding laser light, and a plurality of optical fibers whose emission ends are arranged two-dimensionally.

Images